Telephone system



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. Aug. 28, 1934. SAUNDERS TELEPHONE SYSTEM Filed June 8, 1932 SSheets-Sheet 3 Inufnn :Jr' Nur'man H. saundar's Patented Au 28, 1934 1,971,505 TELEPHONE SYSTEM Norman H. Saunders, Chicago, 111., assignor, by mesne assignments, to Associated Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application June 8, 1e32, Serial No. 615,970 20 Claims. (c1. 179-18) This invention relates to telephone systems in general and particularly to telephone systems in which connections are completed through the medium of automatic switches. The object of the invention is to improve the switching apparatus required for the establishment of local and toll connections in such systems.

General description The switch train to which the improved features of the invention have been applied include toll selectors and combination local and toll connectors. These switches are adapted to cooperate with' other well known switching apparatus and to constitute therewith a complete automatic telephone exchange system.

The toll selectors have been improved by the.

introduction of a 'more efficient and reliable testing circuit wherein a polarized relay tests for a definite potential to indicate an idle trunk. Another feature is the arrangement for registering the number'of calls attempted to trunk groups in which all trunks are engaged. A further feature is the arrangement for switch- 0 ing over from the primary to the secondary operating stage. I

The connectors have been improved by the introduction of a more reliable testing circuit for determining the idle or busy condition of the called lines. Another featurev is the improved wiper-selecting arrangement for determining which one of two sets of wipers is to be used in a connection. Another featureis the arrangement for switching over-from one operating stage to the succeeding operating stage. Another feature is the arrangement which permits the ground connection to the battery-feed relay to be kept open when the connectors are not in use, thereby preventing electrolytic action in the relay winding. A further feature is the arrangement for controlling the supervisory signals according to the class of connection extended over a connector.

While the various features above discussed have been illustrated in connection with specific types of switches, it will be appreciated that certain of these features have a much wider application. The scope of the invention accordingly is not limited by the particular embodiment in which it has been shown, but is defined in the appended claims.

Description of drawings The accompanying drawings comprising Figs. 1 to 3, inclusive, show sufficient circuits 0i a system embodying the invention to permit the same to be readily explained and understood.

Fig. 1 shows a toll operator's cord circuit C, a toll-transmission selector TS, and a toll-intermediate selector IS.

Fig. 2 shows a combination local and toll connector C for extending connections to individual lines.

Fig. 3 shows a combination local and toll connector C1 for extending connections to party lines. I

Referring now to Fig. 1 there is shown the calling end of an ordinary cord circuit C. The cord circuit of which only a part is shown may be of any suitable type provided with a polarized relay for controlling the supervisory signals. The cord is provided with a plug P for connectcatsuit ing the same with trunks extending to transmission selectors, such as the selector TS, at the automatic exchange. The selector TS which is a two-motion Strowger switch, has access to trunks extending to toll-intermediate selectors of which the selector IS has been shown. Both of the toll selectors are provided with testing relays of the type disclosed in Pye PatentNo. 1,673,884, granted June 19, 1928. The characteristicsmf thesere'lays are clearly described in the patent and will be discussed in detail hereinafter. The intermediate selector IS and other similar selectors have access, together with the local selectors of the automatic oflice, to trunks extending to combination local and toll connectors, such as those shown in Figs. 2 and 3.

Connector C-shownin Fig. 2 is accessible over the two branches of the incoming toll-intermediate selectors, local selectors, respectively. The operating characteristics of the switch are determined by the route over which a connection is extended thereto. The switch is equipped with two separate sets of wipers and accordingly has access to two hundred different subscribers lines. Wiper selection is controlled by relays in the switch which respond to impulses dialled by a calling subscriber or operator.

In Fig. 3, there is shown a combination local and toll party line connector G1, which is accessible to toll selectors and local selectors over separate branches of the incoming trunk, respectively. This switch also operates as a local or a toll switch, depending on the route over which a connection is extended thereto. The switch is provided with two separate sets of wipers which give it access to two hundred different party lines. Wiper selection as well as ringing current selection is made by means of an auxiliary switchassociated with the connector.

Detailed description The operations involved in establishing various types of connections over the circuits illustrated in the drawings will now be described in detail to more clearly bring out the novel features of the invention.

Initiation of a toll call Line relay 11 of the transmission selector is energized over a circuit which may be traced from battery, upper winding of the relay, vertical off-normal contacts 16, contacts 29 and 28, resistance, lower left-hand winding of repeating coil R, trunk conductor 4. tip contacts of the jack and plug, upper normally closed contacts of the key K, winding of polarized relay 1, lower contacts of the key K, ring contacts of the plug and jack, trunk conductor 3, upper left-hand winding of repeating coil R, through the resistance and contacts 21 to ground. Relay 1 does not operate at this time due to the direction of current flow in its winding. Relay 11 on operating completes an obvious circuit for relay 12 at contacts 40. Relay 12, which isprovided with a copper sleeve to make it slow-releasing, operates, short-circuits off-normal contacts 16 at its upper contacts, prepares the impulsing circuit at contacts 42, prepares the test circuit at'contacts 44, and at contacts 45 completes circuits for the lower windings of relays 5 and 14. The circuit of relay 5 includes contacts 54, eleventh position contacts RC, and contacts 26 and the lower winding of the relay. Relay 13 whose upper winding is connected in parallel with relay 12 by way of contacts 52 and vertical ofi-norm'al contacts 1'7, operates and prepares a circuit for its lower winding and the vertical magnet in parallel at contacts 49. Relay 5 operates over the circuit above traced and opens a point in the circuit of relay 6 at its upper contacts. The transmission selector is now ready to respond to impulses from the operator's calling device.

Setting the selectors The calling operator now operates key K to v the right, thereby bridging the calling device CD across the trunk conductors in place of the polarized relay 1. The operator then dials the first digit of the called number, interrupting the,

circuit of line relay 11 at interrupter contacts 2 of the calling device CD. Relay 11 responds in the usual way and transmits a corresponding series of impulses by way of contacts 41, 42, and

49 to vertical magnet VM and the lower winding of relay 13. The vertical magnet raises thelay 13 is slow releasing, however, and the impulses received by the lower winding, maintain the relay operated throughout the series of impulses.- It will also be noted that the original energizing circuit of relay 11 is opened at oif-.

normal contacts 16, however, a new circuit for the relay is maintained over the upper contacts of the relay 12.

Shortly after the last impulse of the series, relay 13 releases and completes a circuit for the rotary magnet RM by way of contacts 40, contacts 52, vertical off-normal contacts 16, contacts 48, and interrupter contacts 62. The rotary magnet energizes and steps the wipers in on the first set of contacts in the called level. The selector now tests for the idle or busy condition of the trunk terminating in this set of contacts. As previously stated, the lower winding of relay 14 was energized when relay 12 operated. Relay 14 does not operate over its lower winding alone and requires a specific potential on its upper winding to bring about its energization. This potential in the present instance is battery through the low-resistance winding of a relay in the switch ahead. Assuming that the trunk is busy either due to the prior seizure by another switch or due to the operation of the busy key of the switch associated with the trunk which opens the test circuit, relay 14 will find no operating potential and consequently will not operate. The rotary magnet, upon energizing as described, opened its own circuit at contacts 62 and, upon deenergizing it again closes its circuit so that it now reoperates and advances the wipers a second step. This buzzer-like action continues until an idle trunk is found, which, for example, may be the trunk comprising conductors 63-66 terminating in intermediate selector IS. When the wipers engage the contacts terminating this trunk a circuit is completed from battery through the low resistance upper winding of relay 74, vertical off-normal contacts 69, busy-key contacts BK, release trunk conductor 64, test contact and wiper 59, upper winding of polarized relay 14 and contacts 44 to ground. Relay 14 operates very quickly under these conditions and opens the rotary'magnet circuit at contacts 52. Direct ground is applied to the test wiper by way of contacts 53 and the two windings of the relay are connected in series and a control circuit is extended from the transmission selector to the intermediate 1 selector.

In the selector IS relay 74 operates from ground on the release trunk and prepares various circuits including a circuit for its own lower winding and vertical magnet VM in parallel at contacts 80. A circuit is also completed for line relay 72 of selector IS which may be traced from battery, upper winding of the relay, eleventh position rotary contacts 67, contacts 85, trunk conductor 63,- wiper 58 of transmission selector TS, upper contacts of relays 14 and 11, contacts 32, upper right-hand winding of repeating coil R, contacts 23, upper winding of relay 5, lower right-hand winding of repeating coil R, contacts 39 and 56, wiper 61, trunk conductor 66, contacts 92, lower winding of relay 72, contacts 83 and 89 to ground. The initial energizing circuit of relay 5 was opened at contacts 54 upon the operation of relay 14 and the relay is now energized in series with relay 72 of selector IS. Relay 72 operates in series with the upper winding of relay 5 and completes an obvious circuit for relay 73 at contacts 76. Relay 73 operates, applies ground to release-trunk conductor 64 at its upper contacts, prepares the impulsing circuit at contacts '78 and completes a circuit for the lower winding of polarized relay relay 2'5 energizes and opens circuit at contacts 89. Impulse relay at its lower contacts. Relay 75 does not operate at this time.

The operator now dials the second digit of the called number and relay 11 responds as in the previous instance. The loop circuit previously traced for the impulse relay of the intermediate selector is interrupted at the upper contacts of relay 11 and the impulse relay responds accordingly. The circuit of relay 5 is also opened for each impulse but this relay does not restore during the impulsing as it is slow-releasing due to the copper sleeve and copper slug on its core. Relay 72 responds to the impulses and transmits a corresponding series of impulses by way of contacts 89, 77, 78, and to vertical magnet VM, and the lower winding of slow-releasing relay 74. The vertical magnet raises the wipers to the level indicated by the series of impulses. Relay 74 remains energized throughout the series of impulses due to the impulses received by its lower winding although its initial energizing circuit is opened at vertical off-normal contacts 69 when the wipers leave normal position. Shortly after the last impulse of the series, relay 74 restores and completes the circuit of the rotary magnet at its upper contacts. The rotary magnet energizes, steps the wipers in on the first set of the contacts of the called level, and interrupts its own circuit at its interrupter contacts. The selector tests for an idle trunk in exactly the same manner as described for the transmission selector, and when such trunk is found, polarized the rotary magnet 72 is disconnected from the loop at contacts and 92 and the loop is-extended by way of contacts 86 and 91 andwipers 93 and 96 to the line relay of the succeeding switch. The upper winding of relay 75 is short-circuited at'contacts 87 and the control conductor'is connected by way'of contacts to wiper 95.

Assume for example'that the trunk selected is the trunk comprising conductors 218-221 terminating in connector C (Fig. 2). The control loop of the transmission selector is extended over the upper and lower wipers oi the intermediate selector and thence over trunk conductors 218 and 221, contacts 222, 229, 232, and 235 to the upper and lower winding of relay 203. The upper winding of relay 203 has battery normally connected thereto. The lower winding of this relay is connected tothe release trunk conductor of the switch to which ground is now connected by way of busying key contacts 217 and 216, vertical off-normal contacts 212, test conductor 219, test wiper 94 of switch IS, contacts 87 and the upper contacts of relay 73. Relay 202 operates in the above circuit and completes a circuit for relay 204 at contacts 237. The ground on the release trunk also energizes relay 208 which prepares a holding circuit for itself 1 and connects vertical magnet VM to-the impulse circuit of the connector. Relay 204 operates and connects ground directly to the lower winding of relay 203 at its upper contacts, prepares the impulsing circuit at contacts 240 and opens the release magnet circuit at its lower contacts.

Setting connector C The operator now .dials the third digit of' the called number and relay 11 of the transmission switch 'selector repeatswthese impulses to relay 203 of the connector. Relay 203 in turn transmits impulses by way of contacts 238, 240, lower circuit is opened at ofi-normalcontacts 214..

Relay 207 also completes a circuit for the lower winding of relay 206 by closing its lower contacts. The circuit for relay 206 includes control conductor 220 of the trunk, wiper 95 of intermediate selector IS, contacts 90, trunk conductor 65, wiper 60 of. transmission selector TS, contacts 55, and ground at contacts 38. Relay 206 operates, completes a locking circuit for itself at contactsx249, prepares a new circuit for relay 208 at its lower contacts, and prepares a circuit for the supervisory lamp L1 at contacts 248.

Shortly after the last impulse of the series relay 207 restores and opens the holding circuit of relay 208. Relay 208 restores and prepares the rotarymagnet circuit at contacts 260. The

operator now dials the-fourth digit of the called number and the impulses are repeated as before to relay 203. Each time relay 203 restores an impulse is transmitted over the previously traced impulse circuit which has now been extended by way of contacts 260, .266, and 282 to rotary magnet RM. Relay 207 again energizes and remains energized throughout the series of impulses and at this time completes a circuit by way of contacts 250 and 258, resistance 295, upper winding of marginal relay 211 to battery. Relay 211 when energized over its upper winding in series withresistance 295 energizes only partially and closes contacts 279 which are designated by the Roman numeral I. The closure of these latter contacts prepares a circuit for operating therelay fully upon the release of relay 207 as will be explained subsequently. The rotary magnet responds to the impulses transmitted by relay 203 and rotates the wiper stepby-step to the bank position in which the contacts of the called line are accessible.

Shortly after the last impulse of the series transmitted to the rotary magnet, relay 207 will restore and complete the circuit for energizing relay 211 in its second step. This relay upon energizing completely locks by way of contacts 279 and 278 and vertical off-normal contacts 215. The impulsing circuit previously traced to the rotary magnet is switched over at contacts 281 to two step relay 209. The lower set of wipers, that is, wipers 287-289, are connected up'at contacts 275, 277, and 283/ Further, a circuit is prepared for the lower winding of relay 211 at contacts 280. The connector is provided with two separate sets of wipers and two different lines are accessible in each bank position. The particular one of these lines to be selected will depend upon the last digit dialled by the calling operator. The final digit of the number may be either the digit 1 or the digit 2,

, depending on the set of wipers required. As-

sume first that the digit 1 is dialled and repeated by the transmission selector to relay 203. Relay 203 on releasing completes a circuit from ground, contacts 238 and 240, lower contacts of relay 205, contacts 272, 260, 266, and 281', lower winding of relay 209 to battery. Relay 209 operates only in its first step, thereby preparing a circuit for both windings in series at contacts 264. At the termination of the impulse, relay 203 operates and removes ground from the impulse circuit and relay 209 operates in its second step over its two windings in series. The original operating circuit of relay 211 is opened at the upper contacts of relay 209, a point in the test circuit is closed at contacts 263, and the impulse circuit is transferred by way of contacts 265 or 280 to the lower winding of relay 211. In case no further impulses are transmitted, as will be the case in the present instance, the connector will test over the lower test wiper as will be explained subsequently.

In cas the last digit of the number had been the digit 2, a second impulse would be transmitted over the impulse circuit to energize the,

lower winding of relay 211. The two windings of this relay are difierentially wound, that is, they oppose each other and consequently the result of the second impulse is to restore relay 211 to normal position. The relay on releasing opens the circuits of both of its windings and remains normal regardless of any subsequent impulses which may be transmitted. The set of wipers comprising wipers 285, 286, and 290 is connected up and the test proceeds in the same manner as over the other set of wipers.

Relay 207 energizes during the transmission of the last impulse or series of impulses as previously explained and prepares the test circuit.

After the dialling of the final digit and before the release of relay 207 which is slow releasing, test relay 205 is connected by way of resistance 294, contacts 252 and 263, upper winding of relay 210, and either of contacts 276 or 277 to test wiper 286 or 289. Assuming that the called line is busy when the connection is extended there will be ground on the test contact encountered by the active test wiper and relay 205 will partially energize. Under these conditions relay 205 closes only contacts 245, thereby preparing a circuit for operating the relay fully upon the release of relay 207. The resistance of relay 205 is such that relay 210, is not operated. When relay 207 restores after a slight delay, a circuit is completed by way of contacts 245, 243, and 253- for operating relay 205 fully and the relay locks by way of contacts 245 and 244, to ground at contacts 239. The busy signalling circuit is closed at the upper contacts of the relay, a circuit is completed at contacts 242 for relay 201, and the impulsing circuit is opened at the lower contacts of the relay. Relay 201 operates, disconnects relay 203 from the control loop at contacts 222 and 229 and connects the loop through to the talking conductors of the connector at contacts 223, and 228. Battery feed relay 202 is disconnected from the talking conductors of the switch at contacts 224 and 227.

A circuit is prepared for relay 204 and the lower winding of the relay 202 at contacts 225 and the local holding circuit of relay 206 is opened at contacts 226.

The disconnection of relay 203 from the control loop opens the holding circuit of the relay 5 of transmission selector TS and that relay restores. Relay 5 completes an obvious circuit for relay 6 which operates and by opening contacts 21 and 28 and closing contacts 20 and 27 reverses the battery and ground connections to the incoming trunk by reversing the connection of relay 11 with respect to the trunk conductor. Relay 6 disconnects the upper winding of relay 5 from the control loop and connects the two windings of battery-feed relay 7 thereto. Referring now to the connector, ground is intermittently applied to the upper talking conductor by way of the busy tone interrupter, contacts 247, upper contacts of relay 205, contacts 223, conductor 218, wiper 93 of switch IS, contacts 86, conductor 63, wiper 58 of switch TS, upper contacts of relays 14 and 11, contacts 32, upper right-hand winding of repeating coil R, contacts 24, upper winding of relay 7 to battery. Relay 7 operates intermittently and on each operation completes an obvious circuit for relay 8. Relay 8 operates intermittently to disconnect relay 11 from the incoming trunk by opening contacts 29 and 31. The release of the connection is prevented by the closure of a holding circuit across the two windings of relay 11 by way of contacts 30 of relay 8. In the operators cord circuit polarized relay 1 operates in response to the reversal of battery which takes place upon the operation of relay 6. The intermittent disconnection of relay 11 from the trunk conductors causes the polarized relay to energize and deenergize and thereby light the 'supervisory lamp intermittently. This gives the calling operator a distinctive visual signal indicating that the called line is busy. The operator is then expected to release the connection as will be explained subsequently.

Assuming that the called'line is' idle when a connection is extended thereto as described above, the following operations'take place. An idle line is characterized by-the presence of battery potential on the test contact, the battery being normally connected thereto through the winding of the cut-off relay of the lineswitch. After the dialling of the last digit of the called number the test circuit including busy test relay 205 will be completed as before described. The test relay does not operate due to the battery potential encountered by the test wiper. When relay 207 restores shortly after the last impulse of the series, the test circuit is switched from battery through relay 205 to ground at contacts 239, and relay 210 operates in series with the cut-oil relay of the subscribers lineswitch. Relay 210 completes the ring-backtone circuit at its upper contacts, prepares the ringing circuit at contacts 267 and its lower contacts, completes a circuit for relay 201 at contacts 268, prepares the circuit for supervisory lamp L1 at contacts 269, applies ground directly to the test wiper at contacts 270, completes a locking circuit for itself at contacts 271, opens the impulsing circuit at contacts 2'72, and completes the circuit of relay 208 at contacts 273. Relay 201 operates to connect the lower winding of relay 202 and relay 204 in series and to disconnect relay 203 from the line as was described for a call to a busy line. Relay 208 operates and opens the ringing circuit at contacts 254 and 262, thereby placing the signalling of the called subscriber under control of the calling operator. The disconnection of relay 203 from the trunk permits relay 5 of the transmission selector to restore and reverse battery over the incoming toll trunk. Polarized relay 1 of the cord circuit operates and closes the circuit of the supervisory lamp at the switchboard to give the calling operator line seizure supervision. f

When the operator desires to signal the called subscriber key K will be operated to the "left; thereby applying ringing current to the toll 38. Removal of ground from the control con-.

ductor permits relay 206 of the connector to' Relay 9 completes an obvious circuit Ior relay 10 which operates, completes a holding circuit for relay 11 at contacts 34, and removes ground from the control conductor by opening contacts restore and open the circuit of relay 208. Relay 208 releases and completes the-ringing" circuit.

which may be traced from the generator or battery, interruptercontacts, upper winding of rlng-cut-oflf relay 206, contacts 254 and 267; and either contacts 2'14 or 275 and the associated wiper 285 or 288, depending on the wiper set used, line conductor 292 through the bell and condenser at. the called substation, line conduetor 291, wiper 287 or 290 of the connector, contacts 283 or 284, lower contacts of relay 210 and contacts 262 to ground. The bell at the called substation rings intermittently.-

When the called subscriber. answers a direct current bridge is closed at the substation and relay 206 operates. Relay 206 locks to ground on the control conductor which ;is'grou'nded as soon as the operator restores the ringing key. Relay 206 also completes the'circult of relay 208 which operates to open the ringing circuit and contacts 254 and 262 and complete the connection between the control loop and the called subscriber's line at contacts 256 and 261.

Relay '1' of selector TS operates over the called subscriber's loop and completes the circuit of relay 8. Relay 8 operates. disconnects "relay 11 from the toll trunk, and completes a local circuit for maintaining the relay operated. The disconnection oi relay 11 from the trunk permits relay 1 of the cord circuit to restore and extinguish the supervisory lamp, thereby giving the operator answering supervision. The operator may then switch the calling party into the connection in the usual way and. disconnect her own telephone set therefrom.

When the called subscriber hangs up at the termination of the call, relays -'7 and 8 restore and relay 11 is again connected to the toll trunk. Relay 1 of the cord reoperates and completes the circuit of the supervisory lamp to give the usual disconnect supervision. The operator may then release the switches involved in the connection by withdrawing the plug from the jack.

Release The called subscriber controls the release of the connection, that is, the operator is not able to release the same by withdrawing the plug of the calling cord from the jack until the subscriber hangs up. This is due to the fact that the called subscriber maintains relays '1 and 8 energized. Relay 8 maintains the holding circuit for relay 11 which in turn maintains the circuit of relay 12 and prevents the switches from releasing.

When the called subscriber hangs up at the termination of a call, relay '7 releases and opens the circuit of relay 8. Relay 8 releases and reconnects relay 11 to the trunk, thereby placing the latter relay under control of the calling operator. The operator may then release the connection by withdrawing the plug of the calling cord from the jack. -The circuit of relay 11 is opened and "the relay restores and opens the circuit of relayl2. Relay 1.2 restores and com-' -pletes theicircuit of the release magnet RLM ofl-normal contacts.

by way of contacts 41,- 43, 51;andthe vertical The releasemagnet restores'the switch wipers to normal position in the usual manner. The opening or contacts 44 and 45 upon the release of relay 12 permits relay 14 to restore.v The return-oi the switch wipers to normal position results in the operation' of the various vertical oil-normal spring contacts. Contacts 15 open the circuit of relay 6 which restores and contacts 16 reconnect the upper winding of relay 11 to the trunk line.

The removal of ground from release-trunk conductor 64 due to the release of switch TS permits relay '15 of selector IS to restore and complete the circuit or release magnet RLM. The release magnet restores the switch wipers to, normal position in the usual manner and upon their return thereto the release magnet circuit is opened at oft-normal contacts 68'. The closure of oil-normal contacts 69 reconnects the upper winding of relay '14 to the release-trunk conductor.

The removal of ground from release-trunk conductor 219 upon the release of the preceding switches permits relay 201 to restore and open the circuit of relays 202 and 204 at contacts 225. These relays accordingly restore and at their lower contacts complete a circuit for release magnet RLM- by way of oil-normal contacts 213. Relay 204 removes ground from the local holding circuit, thereby permitting relay Supervisory signals Returning now to the point inthe connection at which connector C connects with the called line, the operation ofrelay 201, as stated, disconnects impulse relay 203 from the trunk conductors and connects relay 204 in series with the lower winding of relay 202. Relay 208 restores and at contacts 23'? opens the original energizing circuit of relay 204. Relay 204 is now energized in series with the lower winding of relay 202 and ground at its own upper 'contacts. Relay 204 maintains the holding circuit of relay 210 and maintains ground on release trunk conductor 296 to mark the connector busy to local selectors. In addition to the foregoing, relay 204 maintains one open point in the circuit of the supervisory lamp L2 at contacts 241 to prevent the lamp from lighting to give a false supervisory signal. Relay 202 maintains an open point in the circuit of supervisory lamp Ll at contacts 230 to prevent that lamp from lighting and giving a false supervisory signal. In local connections, relay 204 is released and relay 202 remains operated when the calling subscriber hangs up first. This results in the closure of the circuit of lamp L2. The called party on hanging up first releases relay 202 while relay 204 remains operated and completes the circuit of lamp L1.

Toll call to a party line The operations involved in extending a toll call to a party line will be described in connection with a call to substations T1 and T2 (Fig. 3). The operator connects the calling end of a cord with a trunk extending to an idle toll transmission selector for example, the selector TS and dials the first two digits of the number with exactly the same results as described for the previous connection. In this case, however, the intermediate selector will be operated to a level in which trunks extending to the party-line connector are accessible. It may .be assumed that the trunk comprising conductors 315-318 is the trunk selected. Ground is extended over release trunk conductor 317 and. control conductor 316 as the previous case, and the control loop is extended over talking conductors 315 and. 313 as before. The ground on the release conductor by way oi the busy key contacts and vertical off-normal contacts operates relay Relay 33.0 prepares a holding circuit it s contacts 365, completes the impulsing sir o to vertical magnet Vi /Z at contacts 365,

o3: Joint i. the circuit of ring-cutmr contacts 363. The ground on also permits impulse rel y (Ad-j re calling loop and complete for relay 30 1-. Relay 30% Q s ground to the local holding ci upper contacts, applies ground direct the lower winding of relay 303 at contacts prepares the impulsing circuit contacts 33, opens the release magnet circuit at its lower contacts. The dialled impulses are repeated by the toll transmission selector in the usual way and relay 303 follows the impulses and repeats them by way of its lower contacts, contacts 334, lower contacts of relay 305, contacts 381, 333, and 363, winding Of vertical magnet to battery. The vertical magnet raises the wipers step-bystep to the called level. Relay 306 which is connected in parallel with the vertical magnet opcrates on the first impulse and, due to its slowreleasing characteristics, remains operated throughout the series of impulses. The ofi-normal springs operate on the first step of the wipers and among other things, open the original energizing circuit of relay 310. Relay 310, however, remains operated throughout-the series of impulses over a circuit including contacts 365, 361, and 342 to ground on the local holding conductor. I

Shortly after the last impulse of the series, relay 306*releases, opens the previously holding circuit of relay 310 and completes a circuit for relay 310 and the' upper winding of relay 309 in series by way of contacts 353 and 341. Relay 310 remains energized and relay 309 energizes in this circuit, the latter relay transferring the previously traced impulse circuit to rotary magnet RM by way of contacts 362.

The operator now transmits the fourth series of impulses which are repeated by the transmission selector to impulse relay 303. Relay 303 repeats the impulses to rotary magnet RM which rotates the wipers of the switch step-by-step to the contact position in which the called line is accessible. Relay 306 operates in parallel with the rotary magnet, opens the circuit over which relays 309 and 310 were being held operated at contacts 341, and completes a holding circuit for the lower winding of relay 309 alone at contacts 342. Relay 310 restores and prepares the circuit of the stepping magnet SM of the auxiliary switch. Relay 309 remains energized throughout the series of impulses. The release of relay 310 completes an operating circuit for relay 307 from. the grounded control conductor and contacts 345 and 368. Relay 307 completes an obvious locking circuit for itself, opens a point in the circuit over which relays 309 and 310 were previously energized, and opens the ringing circuit.

Shortly after the last impulse of the series, relay 306 restores and opens the holding circuit of the lower winding of relay 309. Relay 309 restores and transfers the impulsing circuit by Way of contacts 363 and 367 to stepping magnet SM of the auxiliary switch. The value of the final digit of the number will depend both upon the particular one of the two lines accessible the ban position to which the switch wipe have been set and on the particular p the called line with which a connection is de For example the party 1 on the line accessthe upper set 1 while t will be called by t i is dialled, in-ic at station T2. T repeater magne Sl advances wipers 33 auxilia J S'v 'tch to second 1 banks. J06 operates p with he stepping magnet and prepares tn circuit contacts 343. At the end of the se of impulses and before relay 306 has had to restore, the called line tested for its busy or idle condition over a circuit which may traced from test wiper 386, upper winding of relay 3121, contact and wiper 392 of the auxiliary switch, contacts 343, resistance 313, winding of relay 305 to battery. In case the called line busy there will be a ground on the test contact and relay 305 will operate in its first step closing only contacts 338. When relay 306 releases after a slight delay, a circuit will be completed independent of resistance 313 to operate relay 305 completely. Relay 305 closes the busy signalling circuit at its upper contacts, completes a circuit for relay 301 at contacts 336, completes its own locking circuit at contacts 339, and opens the impulsing circuit of its lower contacts. The calling operator is given a busy signal due to the intermittent connection of ground to the upper trunk conductor by way of contacts 350, upper contacts of relay 305 and contacts 323.

In case the last digit of the number is a 7 for example, instead of 2, as explained previously, the test circuit will be completed over the seventh contact engaged by wiper 392, the upper winding of relay 311 and test wiper 383. The operation of the busy relay 305 will be exactly the same as in the prior connection in case the line is busy.

In the case of a call to an idle line, the test relay does not operate in either of the test circuits previously described, and, when relay 306 releases shortly after the last impulse of the series, a circuit is completed for the upper winding of the switch through relay 311 or 312. In case relay 312 is included in the circuit as will be the case for a number ending, in the digit 2, this relay operates and completes the ring-back-tone circuit at its upper contacts, connects up wipers 382 and 384 at contacts 374 and its lower contacts, completes a circuit for relay 301 at contacts 375, prepares the circuit for supervisory lamp L1 at contacts 376, completes the pick-up circuit at contacts 377, ap-

' circuit above-mentioned above instances,

, at contacts 380, and opens the impulsing circuit at contacts 381. 1

At this point it may be noted that the pick-up is provided to control the start of ringing. In case the ringing used for signalling purposes is of the so-called code type, that is, consists of various codes of ringing current of a single frequency, it is necessary to prevent ringing current from being applied to the line until the interrupter is at the beginning of a code. This arrangement is well-known and pick-up conductor 3'78 in this case would be "connected to the pick-up conductor of the code interrupter. In the case of a toll call, however, the pick-upcircuit is not effective since it is open at contacts 352. Accordingly, no ringing will take place until the operator exchanges the usual ringing control and the code interrupter is in the proper position.

In the case of a system using harmonic ringing, that is, a different frequency for signalling each of the parties on the line, the pick-up circuit above described is not necessary. Relay 310 must be operated, however, and in this case the contact spring of relay-279 is connected directly to ground instead of to the pick-up conductor 278. This arrangement makes it possible to use the same connector for either code or harmonic ringing with a very simple change consisting of the switching of the connection to one spring of relay 312.

Assuming that the last digit of the called number was the digit 7, we have the followingoperation in case the called line is idle. The test circuit, as previously explained, will include the seventh contact of wiper 392 of the auxiliary switch, upper winding of relay 311 and test wiper 383. When the line is idle, relay 305 does not operate and after relay 306 releases the circuit is completed for operating relay 311. Relay 311 connects up line wipers 385 and 387 at contacts 369 and 3'72, applies ground directly to test wiper 383 at contacts 370, and completes a locking circuit for itself and an energizing circuit for relay 312 at contacts 372. Relay 312, accordingly, operates and closes the various circuits described for its operation in the previous instance. 7

Upon the connector establishing a connection with 2. called line, as described in any of the a circuit is completed for relay 301 and that relay operates to disconnect impulse relay 303 from the trunk and to shortcircuit the talking condenser of the switch. The lower winding of relay 302 is connected in series with relay 304 at contacts 325. The disconnection of the impulse relay of the trunk permits the restoration of supervisory relay 5 of the transmission selector and line seizure supervision is returned to the calling operator in the usual way. Relay 303 of the connector restores and opens the original energizing circuit of relay 304. Relay 304 remains energized in series with the lower winding of relay 302 and the latter relay also operates. Relay 304 maintains ground on the various holding circuits and maintains an open point in the circuit of supervisory lamp L2 to prevent a false supervisory signal. Relay 302 opens a point in the circuit of supervisory lamp L1 to prevent this lamp from giving a false supervisory signal.

The calling operator initiates the ringing, as previously explained, by removing ground from the control conductor at the transmission selector, which permits relay 307 of the connector to restore. Relay 307 completes the pick-up circuit at contacts 352 and relay 310 operates at the proper time to complete the ringing circuit. Ringing current is now applied from the selected generator lead G1G5, wiper 391 of the auxiliary switch, and in the case of an odd digit, over the resistance, lower contacts of relays 310, 308, and 307, contacts 373 or thelower contacts of relays 311 and 312, wiper 387 or 384, over one side of the called line through the bell and condenser at the substation, back over the other side of the line, and either back over the other side of the line, and either wiper 382 or 385, contacts 369 or the upper contacts of relay 311 and contacts 374, contacts 346 and 345, and upper winding of relay 307. to battery. In case the last digit of the called number is an even digit, the ringing current will be applied over the lower contacts of relay 306, contacts 358, winding of relay 308 to battery. This ringing current on which ground is superimposed energizes relay 308. Relay 308 looks to ground on the local holding conductor and transfers the ringing circuit by way of contacts 357, resistance, lower contacts of relay 310, contacts 356 and 346, and by way of contacts 369 or the upper contacts of relay 311 and contacts 374 to wiper 382 or 385 of the connec-v tor and thence over the called line. The return circuit for the ringing current includes one of the lower wipers of the connector, lower contacts of relays 311 and 312 or contacts 3'73, lower contacts of relay 307, contacts 359, upper winding of relay 307 to battery. It will thus be seen that the positioning of the auxiliary switch accomplishes four different functions, namely the selection of the particular ringing current to be used, theselection of the set of wipers to be used, the selection of the side of the line to which the ringing current is to be applied, and the closure of the circuit of one or the other of the switch through relays.

When the called subscriber answers a direct The release of the'connection-is the same as for the previously described connection to an individual and is initiated by the. called subscriber restoring his receiver and the operator withdrawing the plug of the calling cord from the jack. The removal of ground from the release trunk and holding conductors permits relays 301 and 307 to restore. Relay 301 opens the circuit of relays 302 and 304 and these relays restore. Relay 304 opens the circuit of relays 308 and 311 and the latter opens the circuit of relay 312 and these relays restore. The circuits for release magnet RLM of the connector and release magnet ARM of the auxiliary switch are closed by way of the lower contacts of the relays 302 and 304 and the respective off-normal contacts. These magnets restore the wipers to stop a selector on the trunk leading to this.

. 1 cal circuit of the release magnet.

normal position in the usual manner, and the switches are ready to respond to the next call.

Local calls The operation of the connectorswitches in local calls is generally the same as in toll calls except for the differences to be pointed out hereinafter. When .a connection is extended to connector C (Fig. 2), for example, by a local selector which has access thereto over the trunk comprising conductors 294-296 the connector operates as follows. Ground is fed ahead over release trunk conductor 296 and energizes relay 208. This ground also permits relay 203 to operate over the calling loop and complete a cir cuit for relay 204. Relay 20 i returns the ground on the release trunk conductor to hold up the preceding switches and this ground by way the contacts of the busy key 23K and the vertiofi -orrnal contacts marks the connector busy to a tell selectors.

response of the switch to the dialled pulses is exactly the same as for a toll co tion and will not be described in detail. It should noted, howev hat relay 208 is not operated during vertica movement or the switch since there i no circuit over control conductor Sn the first vertical step of the wipers cit-normal contacts 212 separate toll release trunk conductor .19 from local release conductor 298. The connector is still busy as far as the toil selectors are concerned since low impedance relay 208 and its battery connection has been disconnected and the switching relays of the toll selector are unable'to operate and switch.

The called line is tested in the same manner as for a toll call and if the line is busy relay 205 operates and locks and connects the busy tone to the upper talking conductor by Way of contacts 246 and the upper contacts of relay 205. Since the toll and local release trunk conductors have been "separated, as above described, and since thereis no ground connection to conductor 219, there will be no circuit for relay 201 and, accordingly, that relay does not operate as it did in a toll connection. Impulse relay 203 remains operated over the loop of the calling line and maintains .the connector in'operated condition. In the meantime the subscriber is given the busy tone to indicate that a connection with the wanted line is impossible, and

called subscriber's loop and at its lower contacts completes a circuit for relay 208. Relay 208 operates and opens the ringing circuit at contacts 254 and 262 and at contacts 256 and 261 extends the calling line through to battery-feed relay 202. Relay 202 operates. and reverses the connection of relay 203 with respect to the trunk conductors. Relay 202 also opens the circuit of supervisory lamp L1, closes a point in the circuit of supervisory lamp L2 and opens a point in the At the termination of a call, one or both of the subscribers hang up and in the latter case the entire connection is released. In case the called subscriber hangs up first, relay 202 restores and at contacts 230 completes a circuit for supervisory lamp Ll. Relay 203, however, remains energized'over the calling line and prevents the release of the connection. Lamp Ll glows to notify the exchange attendant that a connector is being held by a calling subscriber after the calling subscriber has hung up. When the called subscriber finally hangs up, relay 203 releases and opens the circuit of relay 204. Relay 204 removes ground from the release trunl: conductor and from the local holding conductor and closes the circuit of the release magnet. The release magnet operates to restore the switch wip s to normal in the usual man lions relays or" the connector to norma;

In case I subscribes: hangs up relays 205 e 2 release and relay T61 r the loop of the c subscribe- .Te removes ground cm. the relea e local trunk.

local holding conductor or.

circuit and 269, 248, and 231. In addition, relay 202 op the circuit lamp L1 at contacts 230, the circuit of supervisory lamp L2 at co 236, and opens a point in the circuit of t lease magnet. The removal of ground from the local release trunk conductor permits the preceding switches to release. however, cannot be seized in a new connection, due to the fact that relay 208 and its associated battery is not connected to the trunk, as oil-normal contacts 214 are open. Lamp L2 glows to notify the exchange attendant that a connector is being held by 2. called subscriber who has failed to hang up after the calling subscriber has withdrawn from the connection. When the called subscriber finally hangs up, relay 202 releases and opens the holding circuit of the various operated relays and completes the circuit of the release magnet. The release magnet operates to restore the switch wipers to normal position in the usual manner.

It may be noted that during a connection with either a busy line or an. idle line, relay 201 will be connected to test conductor 219 of the toll trunk. Relay 201 is a high-resistance relay and does not energize the test relay of a selector sufliciently to stop a switch on the trunk and, consequently, toll selectors will pass over this trunk. Relay 201 is somewhat slow to operate and the momentary application of ground to conductor 219, as a toll selector tests the trunk, does not operate the relay. However, a slight operation will be of no consequence since the selector will immediately pass by the trunk and restore the relay to normal condition.

The extension of a local connection over connector C1 (Fig. 3) is exactly the same as for a toll connection except for the diiferences due to the absence of ground on the toll-test and control conductors. These differences were fully explained in connection with the individual line connector and need not be repeated. It is surficient to note that relay 307 does not operate until the called subscriber answers and that relay 301 does not operate at any time during the connection. Relay 303 feeds talking battery to the calling subscriber, relay 302 feeds The local trunk,

r CU All-Trunks busy metering In the preceding examples it is assumed ineach case that the selector found an idle trunk in the called group. The operation resulting from the failure to find an idle trunk will now be described. Assuming first that selector TSv (Fig. 1) has been'operated to a level in which all trunks are busy, the selector will rotate, as described in previous connections. In this case since no idle trunks are available, the wipers will be stepped to the eleventh position. A set of contacts are provided in this position to which no trunk is connected. The contact accessible to the lower wiper, however, is connected to an overflow or all-trunks busy meter. When the wiper reaches theeleventh position the eleventh-position cam contact designated RC operates with the results that the circuit of relay 5 is opened and the interrupter INT is connected to the upper talking conductor of the switch. Relay 5 restores and completes a circuit for relay 6. Relay 6 reverses the battery and ground connections to the toll-trunk and connects 'up battery-feed relay '1. The ground intermittently applied to the uppertalking conductor of the switch by the interrupter operates relay '7 intermittently and this relay operates relay 8 which periodically opens the trunk as explained for attempted toll calls to busy lines. The supervisory lamp at the operators position is flashed to give the all-trunks busy signal. A further result of the operation of the elevenposition cam contact is the connection of the upper winding of relay 13 in parallel with release relay l2 and relay 13 operates. After noting the busy signal the operator will release the connection by withdrawing the'plug P'from the jack J thereby opening the circuit of relay ll. Relay ll. opens the circuit of relays 12-and' may serve a number of groups or may be indi-' ,vidual to one particular group, the operation in any case being as described. When relay 13 finally restores, a circuit for the release magnet ELM is completed and the magnet returns the switch wipers to normal position.

The operations resulting from intermediate selector ls encountering a group in which all trunks are busy is substantially the same as the. described for the transmission selector. In this case a circuit is completed through the upper winding of relay 74 to the grounded release trunk conductor. Upon the opening of the control loop from the transmission selector which takes place when the operator disconnects the calling plug from the trunk, relays '72 and '13 restore. During the time required for relay 73 to restore a new circuit is completed for the lower winding of relay '74 which accordingly remains energized ashort time after relay 73 restores. Upon the restoration of relay '13 a metering circuit is completed by way of contacts 89, W, 79, 81, wiper 96 and the eleventhposition contact engaged thereby, to the meter connected to the contact, which will correspond to the meter shown in connection with the transmission selector. Relay 74 restores after a short interval and completes the circuit for the release magnet ELM which returns the selector to normal in the usual manner.

What is claimed is:

1. In an automatic switch having access to a plurality of groups of trunks, a switching relay having a polarizing winding and an operating winding, means for energizing said operating winding responsive to the switch being taken into use to prepare the relay for operation, means responsive to directive control for positioning the switch in selective relation with any one of said trunk groups, means for automatically operating the switch to hunt over the trunks of a selected group, means for energizing said operating winding to operate the relay responsive to the switch-finding an idle trunk in the group hunted over, and means controlled by said relay for interrupting the automatic operation and for effecting the seizure ofthe idle trunk.

2. An automatic switch as claimed in claim 1 in which the switching relay on operating disables its operating winding and completes a circuit for maintaining itself operated over its polarizing winding.

3. An automatic switch as claimed in claim 1 in which a test wiper is connected to the operating winding of the switching relay during the automatic hunting operation and inwhich the connection of the test wiper is transferred to the polarizing winding of the switching relay upon the operation of the relay.

l. In a telephone system, a selector switch, a test wiper for the switch, test contacts accessible to the wiper, said contacts being characterized under different conditions by a connection to "ior stopping the switch.

5. In a telephone system, an automatic switch, a trunk including two talking conductors and a test conductor terminating in the switch, a double-wound changeover relay for the switch, primary and secondary magnets for the switch, means for extending a connection to the switch via said trunk, means responsive to said connection for operating said relay over a circuit including one winding of the relay and said test conductor, means controlled-by said relay when operated for connecting up the primary magnet, means controlled over the talking conductors of the trunk for operating said primary magnet to set the switch, means for opening the operating circuit of said relay at the beginning of the primary operation of the switch, means for completing a holding. circuit including the other winding] of the relay during the primary operation of the switch, means for opening said holding circuit to release the relay upon themeans controlled by said' relay on releasing for disconnecting the primary magnet and for connecting up the secondary magnet.

6. In a telephone system, atoll selector, talking and test wipers for the selector, a line relay,

a release relay and a changeover relay for the selector, means for operating said relays responsive to the seizure of the selector, a group of trunks, means for operating the selector into selective relation with the trunk group, means for releasing said changeover relay to cause the nection, and means responsive to the release of said changeover relay for opening said circuit and for releasing the selector.

7. A telephone system as claimed in claim 6 in which the changeover relay is reoperated due to the closure of contacts adapted to be closed ieed' relay for the switch, supervisory signals,

means for energizing and deenergizing said relays in separate circuit to control said signals in connections of one class, and means for energizing said relays in the same circuit to disable said signals in connections of the other class.

15. In an automatic switch, two sets of wipers, a double wound diflerential relay, means for setting the switch, means for operating said relay over one winding to connect up one set of wipers responsive to the completion of the setting of the switch, and means controlled at will for energizing the other winding of said relay to restore the same and connect up the other set of wipers.

16. In an automatic switch equipped with two sets of wipers and adapted to respond to three series of impulses, a normally open test circuit adapted to operate with either set of wipers, two relays, means for positioning the wipers responsive to the first two series of impulses received, means for operating one of said relays to render one set of wipers effective responsive to the completion of ,the second series of impulses, means for operating the other of said mechanically when the wipers of the selector are relays to complete said test circuit responsive to moved beyond the position in which the last trunk of a group is accessible.

8. In an auto atic switch, incoming conductors including two talking conductors and a test. conductor, a double wound line relay, circuit connections connecting a source of current and one winding of the relay in series to one of said talking conductors, and other circuit connections connecting the other winding in bridge 01' the other of said talking conductors and said test conductor.

9. An automatic switch as claimed in claim 8 in which the connection between the relay winding and the test conductor is opened when the switch is caused to leave its normal position.

10. An automatic switch as claimed in claim 8 in which the circuit connections between the relay windings and the two talking conductors include reversing contacts of a second relay.

11. In a telephone system, lines, an automatic switch, means for operating the switch to connect with a desired one 01' said lines, a test wiper for the switch, test and switching relays in the switch adapted, respectively, to give a calling party a busy signal and to complete a connection to a line, and means for temporarily connecting the wiper and said relays in series to render the relays eflective.

12. In an automatic switch, means for responding to a plurality of series of impulses to select a called line, talking and test wipers, a test relay for determining the idle or busy condition of a call line, a switching relay for connecting up the talking wipers to complete a connection to an idle'called line, and means responsive to the last series of impulses received by the switchdor temporarily connecting said test wiper and said relays in series.

13. An automatic switch as claimed in claim 12 in which the series connection of the test wiper and the two relays is completed immediately after the first impulse of the last impulse series and is maintained for an interval after the last impulse of the series whose length is dependent upon the releasing time of a slowreleasing relay.

14. In a telephone system, a connector switch, means for extending connections of two classes over the switch, a release relay and a batterythe first impulse of the third series, and means for deenergizing said one relay to render the other set of wipers effective responsive to the second impulse of the third series.

17. In an automatic switch equipped with two sets of wipers, a wiper switching relay, a second relay, an impulsing circuit, an operating magnet connected to said circuit, means for operating said first relay to switch wipers and to switch the impulsing circuit from said magnet to said second relay, means for operating said second relay over said impulsing circuit, and means controlled by said second relay for switching the impulsing circuit from itself to said first relay.

18. In an automatic switch equipped with two sets of wipers, means for responding to two series of impulses to set the wipers on contacts of two diiferent lines, means for responding to a third series of impulses to select a set of wip ers, and means for rendering the switch eflective for testing for the busy or idle condition,

of a line immediately after one impulse of the third series has been received.

19. In a telephone system, a connector switch and an associated auxiliary switch, primary and secondary magnets for the connector, a stepping magnet for the auxiliary switch, two changeover relays, means for operating the first 'relay responsive to the seizure of the connector circuit connections controlled by the first relay for connecting up said primary magnet, means for operating the primary magnet to partially set the connector, means for operating both relays in series responsive to the completion of said partial setting, circuit connections controlled by the second relay for connecting up said secondary magnet, means for operating the secondary magnet to complete the setting of the connector, means for releasing both of said relays responsive to the completion of the setting of the connector, and circuit connections controlled by said relays jointly for connecting up said stepping magnet.

20. In a telephone system, a connector having a plurality of sets of wipers, a switching relay for each set of wipers, lines accessible to III said wipers, an auxiliary switch individual to 15th said wipers, a plurality 012 sources of ringing current, means for operating the connector to position the wipers on certain of said lines, means for thereafter operating said auxiliary switch, and means controlled by said auxiliary switch for selecting a particular one of said cur- 

